Question

A particle of specific charge (charge/mass) α starts moving from the origin under the action of an electric field E = E₀ cap k and magnetic field B = B₀ cap k. Its velocity at (x₀, y₀, o) is 4 cap i - 3 cap j . The value of x₀ is: 

Answer 1

q/m = α

Work done by electric field = qE₀x₀= 12m(25–0)

x_o = 25m/2qE₀ = 25/2αE₀ 

Comments

Why do we include only the x component of the displacement even though we are considering the total energy?

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Because work done be magnetic force is zero(Magnetic Force and displacement are perpendicular). Work is a scalar. Net work done (here,by electric force only)=change in kinetic energy.